Oily residue in exhaust

[Diver Down]

I've removed some pieces from one of my engines and noticed that the exhaust elbow and the back end of the turbo (but not the fan) have accumulated some wet oily residue. We tend to spend most of our cruising days running 9-11 kts and probably rarely ever get the RPMs high enough to kick in the turbos. Do these pictures suggest a problem?

[REBrueckner]

Those look pretty much like my 8V71TI components looked the one time I saw inside but of course things depend on many hours have elapsed and whether the turbo has been cleaned/replaced.

I assume you see no smoke at cruise RPM, no air seps nor RACOR CCV's are used. I'm unsure just how those crankcase systems might affect appearance: Supposedly they collect oil mist and benefit the turbos by keeping things clean. I hope so because I added RACORS some time ago. Clean turbo blades, as yours appear to me, are a good sign.

If you boost your RPM's after 4 or 6 or 8 hours of slow cruise and you get a fair amount of smoke for say five minutes, likely you should run a faster or boost RPM a bit more frequently. I used to cruise at 1500 RPM, faster than best for economy, because at about 1100 RPM for example I'd get more smoke at higher RPM than I liked. When running up to 1900 RPM my initial light smoke would clear within a minute.

[Avenger]

Rob, you do realize you're looking at the exhaust side of the turbo which has nada to do with Airseps or CCVs, right?

Diver, what you're seeing there is wet-stacking and assuming you have no other problems like bad injectors, oil consumption or timing issues you need to work those engines harder to burn that off. Put it up once in a while and let it eat.

[REBrueckner]

Whn you say "exhaust"...what are you referring to...you mean the portion headed to the exhaust system, right....why is it unrelated to crankcase systems?


(I may be having a "senior moment" here!!!! Now you have me trying to remember exactly what I did see during disassembly about 12 years ago!!!)

[Avenger]

Crankcase systems seperate oil mist from crankcase vapors which, on most engines, are routed to the intake side of the turbo. Keeping the oil mist out of the gases helps keep oil off the compressor wheel, inter/aftercooler and the rest of the intake system in general. Any oil that gets past that point will get burned in the engine and would not show up in the exhaust. The picture shows the exhaust turbine and elbow, not the compressor (intake) side.

[REBrueckner]

Scrod, thanks, good info...

' wet-staking..." the oily residue...yes
aren't those turbo blades clean..though?? How does that fit together???

"Crankcase systems seperate oil mist from crankcase vapors which, on most engines, are routed to the intake side of the turbo. Keeping the oil mist out of the gases helps keep oil off the compressor wheel, inter/aftercooler and the rest of the intake system in general."

yes, that's all familiar. ....That's the portion of the system I have seen during my own disassembly several times. Like when I removed intercoolers for pressure testing....I'm less clear about the rest...the exhaust side....trying to remember.


I think you are saying that's likely a result of any lube oil getting past rings and unburned/excess fuel rather than crankcase mist, right?? I can buy that, am unsure if I ever really knew that distinction....

[Diver Down]

Scrod, I know you're correct but I was hoping for a different answer! Admittedly, I've been too cheap to run the boat hard so I should have expected the 'wet stacking' problem that comes with cruising at trawler speeds with turbo engines. BTW, the turbos were rebuilt two years ago and I do have CCVs.

[Avenger]

Rob; Yes, it's residue of incomplete combustion. Meaning the engine is just not getting hot enough to fully burn what's in the cylinders so it ends up collecting on the exhaust components which are cooler. Even if the engine used a "road draft" tube, meaning to dump the crankcase vapors into the bilge, the exhaust would still look like this. For crankcase ventilation to cause that by itself there would have to be some serious engine problems.

I see you've been editing while I was typing... the turbine blades are clean because they are fairly thin and have less mass to sink the heat thus they will be significantly hotter than the other components and will burn off residue that the larger parts don't.

[Genesis]

Check the manifold (especially, as those are water-cooled) and pipes in front of the turbo.

If it's there too, wet stacking as noted.

If not, your oil seal in the turbo is leaking.

[Avenger]

Admittedly, I've been too cheap to run the boat hard
A common problem with the motoryacht crowd. :D

You've got a cockpit, so you're halfway to a convertible already. Operate it like one sometimes and that will go away (the wet-stacking and your money). OTOH, now you've got an excuse to have some fun with it once in a while.

[rsmith]

I torched a exhaust valve on one of the 12's onetime when I throttled up after extended trolling. When all that crap starts to burn there is combustion taking place where it was never intended to. All this putting around at slow speed is going to kill a lot of good engines.

[bobk]

How does water jacket temperature play into this. When my starboard 6V92 engine was rebuilt last fall the thermostats were changed from 160's to 170's. That change plus an extra 50-100 rpm above my usual 1000 rpm has reduced the smoke to almost nothing when I run it up. I thought the hotter temps led to less varnish/wet stacking. Is that the case for both or is there still a wet stack issue?

Bob

[34Hatt]

I torched a exhaust valve on one of the 12's onetime when I throttled up after extended trolling. When all that crap starts to burn there is combustion taking place where it was never intended to. All this putting around at slow speed is going to kill a lot of good engines.

Yup SPOOL them UP


Where have I heard that one before ? :)

[Avenger]

How does water jacket temperature play into this. When my starboard 6V92 engine was rebuilt last fall the thermostats were changed from 160's to 170's. That change plus an extra 50-100 rpm above my usual 1000 rpm has reduced the smoke to almost nothing when I run it up. I thought the hotter temps led to less varnish/wet stacking. Is that the case for both or is there still a wet stack issue?

Bob

It's more about cylinder and exhaust temperature. The extra 50-100 RPM may load the engines enough to get the temps up. Have you looked in your exhausts, or are you just looking for smoke? It may still be wet-stacking without significant smoke. Lots of variables here so without pyrometers or inspection we're just speculating. But the extra 10° in jacket water temperature is probably the chicken soup effect. "It can't hurt".

[saltshaker]

My new to me boat has pyrometers and they do tell a lot. Engine temps stay consistent but there is a huge difference between exhaust temps as you start to load the engine. The exhaust temps really start to rise once you get above 1500 RPM.

[REBrueckner]

Michael: I'll pass along the advice I was given some years ago here when I posted about the same issue as you: I forget now who specifically posted it , but they recommended a MINIMUM of 500 degree dry exhaust cruise temperature.

I keep a hand held infrared thermometer aboard, a really useful tool highly recommended. I loosed a section of turbo blanket and tied it back so I could check temperature "on the cheap" with the portable infrared thermometer. Somebody posted that such recorded temps should be only about ten degrees cooler than actual internal...insignificant.

At 1100 RPM and also 1500 RPM after maybe half an hour minimum run time at those RPM's, I checked and found the exhaust temps just about 500 degrees at 1500 RPM. I don't recall the 1100 RPM temp but it was too low; anyway, as I described earlier, the relative absence of smoke at speed up from 1500 RPM cruise made me think about 1500 RPM was about right for my 1972 48 YF with original 8V71TI's.

I was over propped by about 150 RPM, meaning my load at 1500 RPM was almost certainly a bit higher than a boat perfectly set up for 2300 RPM WOT. I kept it that way hoping to load the engines a bit more as I never ran them hard.

Overpropping to achieve some additional efficiency has also been tested by several members and discussed some years ago in great detail, if you are interested. As has running on one engine instead of both engines.

[SKYCHENEY]

Check the manifold (especially, as those are water-cooled) and pipes in front of the turbo.

If it's there too, wet stacking as noted.

If not, your oil seal in the turbo is leaking.

If you have this occurring behind one turbo, then it is probably the oil seal, but behind all 4 then it is wet stacking.

[SKYCHENEY]

Michael: I'll pass along the advice I was given some years ago here when I posted about the same issue as you: I forget now who specifically posted it , but they recommended a MINIMUM of 500 degree dry exhaust cruise temperature.

I keep a hand held infrared thermometer aboard, a really useful tool highly recommended. I loosed a section of turbo blanket and tied it back so I could check temperature "on the cheap" with the portable infrared thermometer. Somebody posted that such recorded temps should be only about ten degrees cooler than actual internal...insignificant.

At 1100 RPM and also 1500 RPM after maybe half an hour minimum run time at those RPM's, I checked and found the exhaust temps just about 500 degrees at 1500 RPM. I don't recall the 1100 RPM temp but it was too low; anyway, as I described earlier, the relative absence of smoke at speed up from 1500 RPM cruise made me think about 1500 RPM was about right for my 1972 48 YF with original 8V71TI's.

I was over propped by about 150 RPM, meaning my load at 1500 RPM was almost certainly a bit higher than a boat perfectly set up for 2300 RPM WOT. I kept it that way hoping to load the engines a bit more as I never ran them hard.

Overpropping to achieve some additional efficiency has also been tested by several members and discussed some years ago in great detail, if you are interested. As has running on one engine instead of both engines.


1500 is too high for slow cruise. If you're going to run there, you might as well put her on plane. You're just pushing water and wasting fuel. There isn't a more inefficient speed than that. 1300 is fine for slow cruise, just run 'em up once in a while to clean 'em out. I'm sick of the BS that is nothing more than repeating things you've read or heard somewhere.

REB, Sometimes you are a little too quick to answer. Sit back and think on it a bit. Jumping in when you don't even fully understand how a turbo works is crazy. Have you ever even had one off before? Have you had one apart? Don't give advice if you're not sure. This is someone's boat we're talking about. Bad advice can cost them money.

Here is the Air Research turbo that we're talking about. I just replaced this one. Notice the hot side (the one that normally has the blanket on it). that is the side we're talking about. Diver had a specific question regarding this part of the turbo and the collector behind it . We weren't talking about the intake side.

http://i134.photobucket.com/albums/q81/skycheney/008-1.jpg

Think before you type. There's no such think as a dumb question, but there certainly is such a thing as bad advice.

[bobk]

Scott, Did you happen to see or hear how my exhaust side looked when Dennis Beaudreau rebiult my transmission? I never thought to look for evidence of wet stacking.

Bob
Chateau de Mer
1981 48MY

[REBrueckner]

"If you have this occurring behind one turbo, then it is probably the oil seal, but behind all 4 then it is wet stacking."

"If not, your oil seal in the turbo is leaking."


Both good observations....

"1500 is too high for slow cruise. If you're going to run there, you might as well put her on plane.'

That depends on the boat and engines.: 1800 or 1900 RPM WAS a nice cruise SPEED for my YF with 8V71TI's, but my fuel consumption grew significantly from 1500 RPM. And my boat really moved at 2,000 or 2100 but I did not want to pay for the further reduction in NMPG and increased maintenance.

Sky: good photo and delineation of components. I had Air Research brand also. That clamp on the left side of the turbine blade housing looks like the one Genesis (I think) has mentioned in past posts. Nope, never disassembled a turbo itself, only removed turbos intact and inspected surrounding components. I had 11 years with the original turbos and they never gave me a problem.

SCROD was helpful to all by explaining where I made a mistake.

[Boatsb]

Bob I will have to ask him.